Aliphatic and cycloaliphatic amines such as trimethylhexamethylenediamine (e.g. the commercially available mixture of approximately equal parts of the 2,2,4- and 2,4,4-isomers), and isophoronediamine (3-aminomethyl-3,5,5-trimethylcyclohexylamine), are frequently used hardeners for epoxy resins, at the present time. A large quantity of epoxy resins reacted in this manner is utilized for protective coatings, castings and electrical applications. When exposed to ultraviolet radiation, e.g. in the form of sunlight, epoxy resins generally, including those produced as described above, show considerable yellowing, often in a matte of hours, eventually becoming brown in color, and further exhibiting loss of gloss and even a tendency to powder. Consequently, the range of applications of such resins, for outside use, is limited.
A principal cause of the undesirable characteristics of epoxy resins just mentioned may be the use of phenolic accelerators as a constituent of hardeners. Salicylic acid is a commonly used accelerator which contains a phenolic group, but other phenolic accelerators which may be mentioned in this connection are, e.g., phenol, cresols and 2,4,6-tris(dimethylamino)phenol, etc.